bpred_unit.hh

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#ifndef __CPU_PRED_BPRED_UNIT_HH__
#define __CPU_PRED_BPRED_UNIT_HH__
 
#include <deque>
 
#include "base/statistics.hh"
#include "base/types.hh"
#include "cpu/inst_seq.hh"
#include "cpu/pred/branch_type.hh"
#include "cpu/pred/btb.hh"
#include "cpu/pred/indirect.hh"
#include "cpu/pred/ras.hh"
#include "cpu/static_inst.hh"
#include "enums/TargetProvider.hh"
#include "params/BranchPredictor.hh"
#include "sim/probe/pmu.hh"
#include "sim/sim_object.hh"
 
namespace gem5
{
 
namespace branch_prediction
{

class BPredUnit : public SimObject
{
    typedef BranchPredictorParams Params;
    typedef enums::TargetProvider TargetProvider;

  public:
 
 

    BPredUnit(const Params &p);
 
    void regProbePoints() override;

    void drainSanityCheck() const;

    bool predict(const StaticInstPtr &inst, const InstSeqNum &seqNum,
                 PCStateBase &pc, ThreadID tid);

    void update(const InstSeqNum &done_sn, ThreadID tid);

    void squash(const InstSeqNum &squashed_sn, ThreadID tid);

    void squash(const InstSeqNum &squashed_sn, const PCStateBase &corr_target,
                bool actually_taken, ThreadID tid, bool from_commit=true);
 
  protected:


    virtual bool lookup(ThreadID tid, Addr pc, void * &bp_history) = 0;

    virtual void updateHistories(ThreadID tid, Addr pc, bool uncond,
                           bool taken, Addr target,
                           const StaticInstPtr &inst, void * &bp_history) = 0;

    virtual void squash(ThreadID tid, void * &bp_history) = 0;
 

    virtual void update(ThreadID tid, Addr pc, bool taken,
                        void * &bp_history, bool squashed,
                        const StaticInstPtr &inst, Addr target) = 0;

    virtual void branchPlaceholder(ThreadID tid, Addr pc,
                                   bool uncond, void * &bp_history);

    bool BTBValid(ThreadID tid, Addr pc)
    {
        return btb->valid(tid, pc);
    }

    const PCStateBase *
    BTBLookup(ThreadID tid, PCStateBase &pc)
    {
        return btb->lookup(tid, pc.instAddr());
    }

    const StaticInstPtr
    BTBGetInst(ThreadID tid, Addr pc)
    {
        return btb->getInst(tid, pc);
    }

    void
    BTBUpdate(ThreadID tid, Addr pc, const PCStateBase &target)
    {
        ++stats.BTBUpdates;
        return btb->update(tid, pc, target);
    }
 
 
    void dump();
 
  private:
 

    struct PredictorHistory
    {
        PredictorHistory(ThreadID _tid, InstSeqNum sn, Addr _pc,
                         const StaticInstPtr & inst)
            : seqNum(sn), tid(_tid), pc(_pc),
              inst(inst), type(getBranchType(inst)),
              call(inst->isCall()), uncond(inst->isUncondCtrl()),
              predTaken(false), actuallyTaken(false), condPred(false),
              btbHit(false), targetProvider(TargetProvider::NoTarget),
              resteered(false), mispredict(false), target(nullptr),
              bpHistory(nullptr),
              indirectHistory(nullptr), rasHistory(nullptr)
        { }
 
        ~PredictorHistory()
        {
            assert(bpHistory == nullptr);
            assert(indirectHistory == nullptr);
            assert(rasHistory == nullptr);
        }
 
        PredictorHistory (const PredictorHistory&) = delete;
        PredictorHistory& operator= (const PredictorHistory&) = delete;
 
        bool
        operator==(const PredictorHistory &entry) const
        {
            return this->seqNum == entry.seqNum;
        }

        const InstSeqNum seqNum;

        const ThreadID tid;

        const Addr pc;

        const StaticInstPtr inst;

        const BranchType type;

        const bool call;

        const bool uncond;

        bool predTaken;

        bool actuallyTaken;

        bool condPred;

        bool btbHit;

        TargetProvider targetProvider;

        bool resteered;

        bool mispredict;

        std::unique_ptr<PCStateBase> target;

        void *bpHistory = nullptr;
 
        void *indirectHistory = nullptr;
 
        void *rasHistory = nullptr;
 
    };
 
    typedef std::deque<PredictorHistory*> History;
 

    bool predict(const StaticInstPtr &inst, const InstSeqNum &seqNum,
               PCStateBase &pc, ThreadID tid, PredictorHistory* &bpu_history);

    void squashHistory(ThreadID tid, PredictorHistory* &bpu_history);
 

    void commitBranch(ThreadID tid, PredictorHistory* &bpu_history);
 
 
 
  protected:
    const unsigned numThreads;

    const bool requiresBTBHit;

    const unsigned instShiftAmt;

    std::vector<History> predHist;

    BranchTargetBuffer * btb;

    ReturnAddrStack * ras;

    IndirectPredictor * iPred;

    struct BPredUnitStats : public statistics::Group
    {
        BPredUnitStats(BPredUnit *bp);

        statistics::Vector2d lookups;
        statistics::Vector2d squashes;
        statistics::Vector2d corrected;
        statistics::Vector2d earlyResteers;
        statistics::Vector2d committed;
        statistics::Vector2d mispredicted;
        statistics::Vector2d mispredictDueToPredictor;
        statistics::Vector2d mispredictDueToBTBMiss;

        statistics::Vector2d targetProvider;
        statistics::Vector2d targetWrong;

        statistics::Scalar condPredicted;
        statistics::Scalar condPredictedTaken;
        statistics::Scalar condIncorrect;
        statistics::Scalar predTakenBTBMiss;

        statistics::Scalar BTBLookups;
        statistics::Scalar BTBUpdates;
        statistics::Scalar BTBHits;
        statistics::Formula BTBHitRatio;
        statistics::Scalar BTBMispredicted;

        statistics::Scalar indirectLookups;
        statistics::Scalar indirectHits;
        statistics::Scalar indirectMisses;
        statistics::Scalar indirectMispredicted;
 
    } stats;
 
  protected:


    probing::PMUUPtr pmuProbePoint(const char *name);
 

    probing::PMUUPtr ppBranches;

    probing::PMUUPtr ppMisses;

};
 
} // namespace branch_prediction
} // namespace gem5
 
#endif // __CPU_PRED_BPRED_UNIT_HH__